This invention relates to a constant pressure mechanism for a portable label printing and applying machine, in which a pressure-sensitive self-adhesive label strip is intermittently delivered in single label lengths on a platen by the squeezing operation of a hand grip and a hand lever. A printing head above the label strip and the platen under the label strip are moved separately but toward each other so as to exert a constant printing pressure on the label strip for highly precise printing.
In conventional label printing and applying machines, the printing pressure of a printing device against a label is liable to vary depending upon whether the hand lever is squeezed strongly and weakly. Further, when the hand lever is squeezed for a long time and then released rapidly, the quantities of ink applied to labels differ even though the printing pressure is made constant. Therefore, invariable precision in printing has never been attained.
In the past, however, such indistinctly printed labels have caused no inconvenience because they are in practice used for human readable labels for price indication and they can be almost read with the naked eye when customers buy several goods or cashiers totalize sales.
In recent years, POS (point of sales) systems have been widely adopted all over the world. In these systems, management data such as stock, sales, the relation between customers and commodities required, calculation of profits, etc. are processed and memorized by electronic computers. In this system, machine readable bar codes or characters for OCR (optical character reader) printed on labels are read out by optical readers connected to computers in place of cashiers. Accordingly, it is necessary that label printing always be precise.
In order to always attain highly precise printing, the type faces of the printing head must be pressed against the surfaces of labels with a constant pressure even when the hand lever is squeezed strongly or weakly. The type faces of the printing head must contact the surfaces of labels for a definite time length with uniform printing pressure no matter what the duration of a squeeze of the hand lever may be. Accordingly, label printing machines having constant printing pressure mechanisms are now demanded.
In connection with the art of constant pressure mechanisms, there have been several applications filed by the inventor hereof:
I. A movable platen system in which a printing head is fixed to the machine frame and a platen is moved through its connection with a hand lever: PA1 II. A movable printing head system in which a platen is fixed to the machine frame and a printing head is moved through its connection with a hand lever: PA1 (1) The platen is moved only to a slight degree so that the type faces are lightly pressed against the labels supported on the platen. Precise printing can be attained without double printing. PA1 (2) The contact pressure of the type faces on the labels is relatively small so that the types may give long service. PA1 (3) Since the platen is only slightly moved, the constant pressure springs also give long service. At the same time, the force necessary for squeezing the hand lever can be reduced, which facilitates the operation of the machine. PA1 (4) A hinged link plate for vertically moving the platen over a long distance is not necessary, so that blocking of the feeding movement of the label strip can be avoided. PA1 (5) The machine can be made easily as the internal mechanism is compact. PA1 (6) The number of required parts is small so that the mechanism can be produced at low cost and can work well without trouble.
U.S. patent application Ser. No. 681,251, filed Apr. 28, 1976, for "Portable Label Printing Machine;" PA2 U.S. patent application Ser. No. 720,225, filed Sept. 2, 1976, for "Print Head Constant Pressure Mechanism for Labeling Machine;" PA2 U.S. patent application Ser. No. 723,556, filed Sept. 15, 1976, for "Portable Label Printing Dispensing Machine." PA2 U.S. patent application Ser. No. 750,845, filed Dec. 15, 1976, for "Portable Label Printing and Applying Machine."